Elevators typically use electromagnetic brakes to stop the elevator car.
As shown in FIGS. 1 and 2, a typical electromagnetic brake for an elevator is shown. The brake has a pair of arms 2a and 2b which pivot about an axle 4. Brake pads 7 are attached at one end of arms 2a and 2b by means of bolts 5. As the brake arms pivot about the axle, the arms move the brake pads into contact with stationary rail 1 to stop the elevator car or out of contact with the rail to release the car for movement.
An axle 9a extends from an other end of arm 2a towards arm 2b. An axle 9b extends from an other end of arm 2b and is received axially within axle 9a. A ferromagnetic body 11a is attached to the axle 9a. Similarly, a ferromagnetic body 11b is attached to the axle 9b. A spring 23 is disposed about the axles 9a and 9b and acts to bias the ferromagnetic bodies 11a and 11b apart. A coil 13 is disposed within a circumferential groove 19 within the ferromagnetic body 11b. The coil is connected to a conventional power source (not shown) via an electrical line 15.
The electromagnet is attached to the elevator cab, as is known in the art.
With this type of electromagnetic brake, when the coil is not energized, the spring urges the brake arms to pivot about the axle 4 thereby forcing the brake pads 7 into contact with the rail. The elevator cab is then effectively stopped from movement. When the coil 13 is excited, the ferromagnetic bodies are attracted to each other, in opposition to the force of the spring, thereby releasing the brake pads from the rail.
If the coil 13 is defective or the power source is disconnected, the ferromagnetic bodies will not overcome the spring force to urge the brake pads out of contact with the rail. Since the spring force keeps the brake pads in contact with the rail, the cab may not be easily moved and elevator passengers may be in the cab for an unacceptable time period.
As a result, a new type of electromagnetic brake is required.